University police chief Gregory T. Fowler identified the alleged gunman as 18-year-old Steven Jones, who was taken into custody by the first police officer who arrived on the scene following the 1:20am (MST) shooting.

The shooting occurred in a parking lot outside Mountain View Hall dormitory at the northeast side of the Flagstaff campus.

University President, Rita Cheng, said in a press conference: "This is not going to be a normal day at NAU. Our hearts are heavy."

The university and Flagstaff police are still investigating, but the university has called the shooting an "isolated and unprecedented" incident and classes will go on as planned.

Student Maria Gonzalez told The Associated Press that she first suspected firecrackers.

She said: "I was studying for an exam so I looked out the window and see two people running, and that's when I realised they weren't fireworks they were actually gunshots.

"How am I supposed to feel safe where I'm learning?"

School public relations director Cindy Brown said the injured were taken to Flagstaff Medical Centre, which said it couldn't release information on their conditions.

Sen. John McCain, R-Ariz., released the following statement Friday morning:

"My thoughts and prayers are with families of the person who was killed and the three others who were wounded in the horrific shooting on the campus of Northern Arizona University in Flagstaff early this morning. I appreciate the efforts of all state and local law enforcement officials, first-responders and school administrators, and continue to pray for the recovery of the injured, as well as all those in the NAU community who have been impacted by this terrible tragedy."

University officials have set up a Family Assistance Center along with support services available to the students, faculty and staff.

The university has more than 25,000 undergraduates, and plays a major role in the northern Arizona city of Flagstaff.

The shooting came on the day Barack Obama was visiting Roseburg, Oregon, where eight students and a teacher were shot and killed last week at Umpqua Community College.

The gunman in the Oregon shooting wounded nine others before turning the gun on himself.